THIS AVALANCHE ADVISORY EXPIRED ON January 20, 2018 @ 5:52 am
Avalanche Advisory published on January 19, 2018 @ 5:52 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Due to strong southwesterly winds and moist snow we have thick, sensitive wind slabs lurking on leeward terrain features and fresh storm snow above 5,000'.  Avoid committing to steep slopes directly below ridge lines on north and east aspects.  Approach any slope over 35° with strong caution in terrain above 5,000'.

How to read the advisory

Due to strong southwesterly winds and moist snow we have thick, sensitive wind slabs lurking on leeward terrain features and fresh storm snow above 5,000'.  Avoid committing to steep slopes directly below ridge lines on north and east aspects.  Approach any slope over 35° with strong caution in terrain above 5,000'.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Southwest winds have created dense and senstive slabs near ridglines and on open exposed terrain features.  You will likely find this problem throughout the weekend above 5,000'.   



Here is what you are likely to see on steep (35°), northeast aspects.  Photo taken near top of Flatiron Mounain in Purcell Range at 5,800'.   

Avalanche Problem 2: Storm Slab
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The latest storm came in very warm and started out as rain up to 6,000'.  It slowly transitioned back to snow as both temperatures and snowlines dropped.  This has left us with the potential to release storm slabs on the highest terrain of the Kootenai where this moisture came in as steady snowfall.  Yesterdays observations revealed that this new snow was bonding well as the temperatures declined.  It was showing a low likelihood of propagation; but, as one gains elevation this snow will increase in depth and cohesion as it is pushed around by the wind.

Avalanche Problem 3: Persistent Slab
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I am grouping all structural snow pack weaknesses together in this problem.  This includes the buried surface hoar (1-2' deep-varies with location) and the deeply buried facet layer resting on the Thanksgiving rain crust.  The buried surface hoar layer was failing with hard force but showing that it is unlikely to propagate into an avalanche. Warm temperatures and time have given it the opportunity to break down and thin into the surrounding snowpack.  The deeply buried facets have also shown steady improvement in strength as well.  They are still easily identified but have not shown much potential to fail for the past few weeks.  The likelihood of triggering this layer will be low unless one were to find a thin spot in the snowpack (particularly in the Purcell Range) or during a drastic change in weather that involves high temperatures and rain at the uppermost elevations.



Pit results taken on Flatiron Mountain showing 2 persistant weak layers in the snowpack.  These weak layers can be found in the East and West Cabinets as well; however, they are much deeper.

advisory discussion

Come join us for a free "Intro to Avalanches" course on Friday the 26th, 7 PM at the Libby David Thompson SAR barn.  This will involve a 2-3 hour class on Friday and followed by a field day at the Keeler Rattle hut Saturday morning.  If you don't have a snowmobile you are welcome to attend the classroom portion and skip the field day.  For more info you can email me at bbernall@fs.fed.us or call Terry Crooks at 293-1618.

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
410 AM MST Fri Jan 19 2018

DISCUSSION: Snow showers will be widespread this morning across
west-central/southwest Montana and central Idaho. Snow levels have
lowered to roughly 2000 feet. Shower activity will likely wane
through the morning, before increasing once again this afternoon 
across all of western Montana and central Idaho as the atmosphere
becomes unstable. Cooler and showery conditions will persist into
Saturday, though additional snow amounts are expected to be light.
A drier period looks likely for Sunday as weak high pressure
briefly builds into the region.

Cooler, showery and generally active conditions are expected to
last into next week, with only brief dry periods. Breezy ridge top
winds will be prevalent from the west for much of the week. Although
it is expected to be an active week for mountain snow, most of 
the storms are expected to be light to moderate in intensity. 
There is potential to see a stronger system by late week. 

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           90%          85%          85%      
Hi/Lo Temps           25 to 30     18 to 23     25 to 30 
Winds(mph)            SW 11        SW 10G21     SW  9G22 
Precip Chc            60           60           60       
Precip Type           snow         snow         snow     
Liquid Amt            0.04         0.06         0.08     
Snow Ratio(SLR)       16:1         17:1         16:1     
Snow Amt(in)          0-1          1            1-2      
Snow Level            2000         2000         2000 
Disclaimer

Avalanche conditions change for better or worse continually. Backcountry travelers should be prepared to assess current conditions for themselves, plan their routes of travel accordingly, and never travel alone. Backcountry travelers can reduce their exposure to avalanche hazards by utilizing timbered trails and ridge routes and by avoiding open and exposed terrain with slope angles of 30 degrees or more. Backcountry travelers should carry the necessary avalanche rescue equipment such as a shovel, avalanche probe or probe ski poles, a rescue beacon and a well-equipped first aid kit.  For a recorded version of the Avalanche Advisory call (208)765-7323.